This invention relates to a batch pack for silver filings for the preparation of a dental amalgam in a laboratory mixing apparatus. More particularly, this invention relates to a foil bag which is inserted in a mixing chamber and exposed to mixing vibration for releasing the contents of the foil bag under the action of the mixing vibration.
In U.S. Pat. No. 4,306,651 issued to the present applicant which patent disclosure is incorporated herein by reference, a multi-component capsule for dental purposes is shown wherein one component is freely contained in the mixing chamber of the capsule and the other component is contained in the foil bag and thereby separated from the one component until the foil bag is destroyed by the mixing vibration. Naturally, it is sufficient to enclose merely one component in a bag so as to insure chemical separation during the storage period. The use of a multi-component capsule for storage and for a single mixing operation involves a certain expenditure which can be avoided where the dentist places silver powder as well as, by means of a dosing apparatus, a corresponding quantity of mercury into a mixing capsule for multiple use, closes the capsule and subsequently mixes the components in a vibration apparatus. While this method is less expensive, inexact dosages may result more readily than with a mechanical pre-dosing, and the physician is exposed to the immediate influence of the mercury.
The present invention concerns the problem of combining the simplicity of the method as known from the use of disposable capsules with the low expenditure involved in the repeated use of the capsule. A solution according to the invention resides in the fact that the powdery component is also enclosed in a separate foil bag which is exposed to vibration and opens under the action of the mixing vibration, with the foil bag consisting of a material having a specific gravity several times lower than that of the powdery component.
The enclosure of both components in respective foil bags permits their optional use, irrespective of whether they are supplied in a disposable capsule or whether they will be inserted by the dentist into a mixing capsule to be used if necessary several times. Furthermore, the enclosure of both components permits an easy and simple dosing by inserting in each case such a number of foil bags containing the components into a mixing capsule in accordance with the desired amalgam amount.
Powder would not be expected to liberate itself sufficiently completely from a foil bag which opens under mixing vibration since such characteristics cannot be expected even of the liquid component under certain conditions. For example, there is the possibility that mercury will not be distributed completely from a sealed metal foil bag as disclosed in U.S. Pat. No. 4,182,447. If the complete emptying of the foil bag appears not to be insured even with liquids under certain conditions, then this would much less be expected as regards the storage of a powder in a foil bag. It is more surprising that the complete discharge of the powdery component is achieved if in accordance with the present invention the specific gravity of the bag material is several times lower than that of the powder. It may be assumed that this effect is due to the fact that in accordance with the physical law of force equals mass times acceleration, the forces exerted by the various vibration accelerations and the substances contained in the capsule are considerably smaller in relation to the specifically lighter bag material than in relation to the powder particles so that the latter is separated from each other by the very different forces acting on them. It may also be of importance in this connection that under vibration conditions the powder does not behave as solid material but behaves very similar to a liquid. This latter characteristic is due to the fact that powder particles get into a relative motion with respect to each other whereby air layers are enclosed between them which terminate the solid connection and put the powder as a whole into a so-called fluidized state, which state is known as being used in another technical field, namely that of the mechanical conveying and handling of powdery material.
It can easily be determined by experiments by how many times the specific gravity of the powder must be greater than that of the bag material. There is to be achieved a density ratio, relative to the solid powder material, of at least 5 and preferably of more than 8.
The invention relates furthermore to a mixing capsule for carrying out the stated method of the vibration mixing of several components contained therein particularly for dental purposes. The mixing capsule contains in a mixing chamber a liquid component tightly enclosed in a foil bag for releasing said component under the action of mixing vibration in a powdery component. The powdery component is contained in a separate foil bag which opens under the action of the mixing vibration with the foil bag consisting of a material having a specific gravity several times less than that of the powdery component by a factor of at least 5 and preferably more than 8.
Finally, this invention relates to a portion package for silver powder or the like powdery dental material intended for a vibration mixing in a dental mixing capsule. In the package, the powder is enclosed in a foil bag, the material of which is specifically several times lighter than the powder and the strength of which is predetermined such that it opens under the action of the mixing vibration in the mixing chamber of the dental mixing capsule.
The enclosure of the powder, particularly the silver powder or the silver filings, in a foil bag has a great advantage that the portion size can be pre-determined with great exactness. Dental amalgam is prepared by the dentist from silver filings and mercury to obtain a more accurate dosage. It is known to prepare batch packs of the two components, which batch packs are together introduced into a mixing capsule which is exposed in a mixing apparatus to a mixing vibration of, for example, 300 Hz. Known batch units for the silver filings consists of pellet-shaped pressings which are supplied loose in a relatively large number in a suitable packaging container. To prevent an excessive loss of their weight due to mutual attrition and to enable them to be handled without a risk of breakage, the pellet-shaped tablets are compressed to a high density which approaches the density of the solid metal to within a few percent. Nevertheless, the formed tablets can suffer an undesirably large weight loss due to attrition, particularly if the tablets are inexpertly handled and remain for a long time in the common container. The tablets also have the disadvantage that under the action of vibration in the mixing capsule the tablets disintegrate sufficiently into reactive powder only in the presence of a pestle.
It is also known to store such tablets in a foil bag such as disclosed in European Published Application 83 106110 wherein at least the attrition loss is eliminated but the need for a pestle is not avoided. Moreover, it is known to introduce the silver filings in the form of a powder into the foil bag. This latter configuration has the advantage that the silver filings are available immediately in the reactive form. Nevertheless, a pestle is required in most cases, namely in order to accomplish destruction of the foil bag. Even though the foil bag can be made so thin that even without a pestle it tears under the acceleration forces exerted by the powder and the adjacent mercury during the mixing vibration, the use of somewhat thicker foil is frequently desirable in order to provide greater safety for good separation of the components and against the formation of relatively small foil residues which might make clean removal of the amalgam more difficult.
It is therefore an object of the present invention to provide a batch pack for silver filings for the preparation of dental amalgam in a laboratory mixing apparatus which is easier to handle. In accordance with the present invention the silver filings are pressed into a briquette for enclosure within the foil package. The density of the briquette is not more than approximately 8 gram/cm.sup.3 and preferably not more than 7.5 gram/cm.sup.3. The density of the pore volume of the briquette is at least approximately 20 percent.
According to a further feature of the present invention, portion packages of the dental material components to be used together can be connected to each other. This presents not only the advantage that the use is simplified since in each case only one portion of the package with both components needs to be inserted in the mixing capsule but also the portioning becomes more reliable since no mistakes can occur in the coordination of component amounts suited to each other. Additionally, several portion packages can be inserted in the mixing capsule at a time, such as for a large tooth filling wherein there is required an amalgam amount greater than that provided by one portion package.
The connection of the two individual portion packages to a common portion package can be achieved in a simple way, e.g., by adhesion bonding. According to another feature of the present invention, the connection between the individual portion packages is obtained in that at least one foil is in involved in the formation of both portion packages. Preferably, even both portion packages are formed integrally by a pair of foils, which are welded together in forming two separate portion pockets.
According to a further embodiment of the invention, two cover foils are welded together with a central foil to form two portion pockets situated on both sides of the central foil.
The destruction of the foil bag containing the liquid component is facilitated by the powdery component being packed in a foil bag combined as a unit with the liquid bag, since the entire powder material substantially simultaneously exerts impact on the liquid bag and thus a stronger effect thereon than simply a powder distributed in the entire space.
There may be provided devices which improve the opening of the foils under the action of the mixing vibration and/or the mixing effect, for example a pestle, which may also be contained in the portion package, or edges or prongs projecting inwards from the wall of the mixing chamber.
If a capsule is to be used repeatedly for the preparation of a dental amalgam, the capsule must be cleaned between individual applications or at least from time to time. Furthermore, the capsule has to be considered a disadvantage in that the prepared mixture must be taken out of the capsule in a relatively complicated way, and in which respect also the remainders of the consumed packaged, likewise contained in the capsule, can be inconvenient. Such a disadvantage can be avoided in accordance with the present invention in that the package foil, destructible by the action of the mixing vibration, together with the portion chamber separated therefrom and including the dental material components, is enclosed by a package casing not destructible by the action of the mixing vibration.
After the mixing process, the mixed material is now contained in the free form within the mixing chamber of the mixing capsule but is still enclosed by the foil bag, wherein merely the inner separating foil has been destroyed. One can therefore simply take the closed portion package out of the mixing capsule, tear the portion package open and take out the mixture by a spatula or squeeze the mixture out between two fingers. Thus, the removal of the mixture is substantially simplified and is achieved without special measures in a fashion wherein the mixture remains hygenic.
The arrangement of the package foil destructible by the mixing vibration with respect to the non-destructible packaging casing can be different. In one advantageous embodiment there are provided for example two foil bags, one of which freely encloses as a covering foil bag the first dental component as well as the destructible foil bag containing the second dental material component. In accordance with another expedient embodiment, it is provided that two foils, together forming the covering foil bag, are welded together on both sides of the destructible foil either to the latter or to each other.
After mixing, the outer package casing which is not destructible by the mixing vibration forms a container for the mixed dental material. In order that the container can be handled more easily, it can be formed according to the invention as a semi-flexible cup-like package portion. The term semi-flexible means that the container retains the cup-shape in a more or less deformed state even if it is held between the fingers in order to be emptied. Its cup-shape facilitates the removal of the mixed material.
Additionally, it may be provided according to the present invention that the package casing is provided with an opening device. An opening device is understood to mean those elements or formations which enable or facilitate the opening process. This includes, for example, gripping lugs projecting outwards from the portions forming the actual package casings so as to allow, for the purpose of opening, a gripping thereof in the exertion of a force. Furthermore, this includes ideal tearing points in notches in the welding edge in which the opening tear may be started.
The portion package according to the present invention can enclose the dental material components without a substantial empty space so that the mixing forces created upon the impact of the portion package during the mixing vibration at the ends of the mixing capsule will be transferred, without being damped, onto the dental material components to be mixed. This applies particularly of a flexible material as used for the non-destructible package casing, which completely transmits the forces to the dental material. Instead of this, it may, however, also be provided that the portion package includes a certain empty space permitting a certain vortexing. This applies particularly if the package casing consists wholly or partially of a semi-flexible or stiffer material.
It may also be expedient that the portion package contains a pestle, i.e., a body of for instance glass, ceramics, synthetic material, which due to its movement within the portion package, caused by the mixing vibration, assists in the mixing of the components. It is not necessary that the two component bags are inserted in the mixing capsule only by the dentist and immediately prior to use, but the invention rather presents also the advantage that the filling of the capsule becomes independent of the dosing and encasing of the components. Finally, there is achieved an advantage wherein it is not necessary to tightly close the capsule, even if the latter is intended for long term storage, such that the components in their bag packages can be sufficiently sealed against atmospheric influences and evaporation of poisonous gases into the atmosphere is prevented.
The foil packages may be provided with imprints, i.e., with statements required under the drug law, such as the name of the manufacturer, weight, durability, date of filing, specification of the materials, etc. The individual foil packages can be lined up as double packages or individually within a strip of similar packages and can be separable from each other and, if necessary, from the strip section provided with the information by perforation or pre-determined breaking points, respectively.
The invention presents considerable price advantages over the known disposable capsules, which mostly have to be additionally prepared for mixture by turning, pressing, or screwing. The encasing of the amalgam powder in foil bags can also be advantageous over the processing in the form of tablets since the latter first have to be compressed which involves cost. Moreover, it can be disadvantageous for some amalgam powders to be compressed tablets. Finally, the abrasion of the tablets may lead to differences in weight. Compared with the use of automatic mixers, the invention involves the advantages of a greater exactness, the amalgams of any kind can be used, so that no maintenance of the apparati is required and so that the dentist is not exposed to mercury vapor.
The portion package of the components to be mixed can be inserted in the mixing capsule at any point of the chain between production, storage and use.
In the context of the invention, both the mixing capsule and the vibration mixers used for dental purposes can be considered to be known. Mixing capsules are elongated containers closed by a removable lid having a length in the order of 3 cm and a diameter on the order of 1 cm. The mixers are formed so that the mixing capsules inserted therein can be reciprocated in their longitudinal direction at a frequency of 300 Hz so that the material contained in the interior of the capsule (the mixing chamber) is flung to and fro between the end walls of the mixing chamber. The volume of the material amounts to only a very small portion of the volume of the mixing chamber. Typical amalgam portions as they are prepared by the dentist in one mixing operation lie between 0.5 grams and 1 gram.
With respect to foil materials, they are particularly suitable synthetic materials, e.g., a polyethelyne foil of thickness on the order of magnitude of 0.05 mm.